Supplemental braking device for a towed vehicle

ABSTRACT

A system and method for braking a flat-towed vehicle based upon a braking pressure of a braking fluid in a braking circuit in the towing vehicle, the method includes measuring a piezoresistor voltage drop across a piezoresistor positioned within the braking circuit such that the piezoresistor voltage drop changes in response to the braking pressure within the braking circuit. Based upon the measured piezoresistor voltage drop, a motor frame duration is retrieved. A clutch engages the motor output shaft to initiate a clutch frame. Upon expiration of a programmed clutch delay, a motor frame initiates by supplying power to a motor. Upon expiration of the motor frame duration, power to the motor is interrupted. The clutch continues to be engaged for the duration of the clutch frame. The clutch releases allowing a capstan attached to the clutch to spin freely relative to the motor output shaft.

RELATED APPLICATION

This is a continuation-in-part of the co-pending application Ser. No.15/345,384 dated Nov. 8, 2016 entitled “Supplemental Braking Device fora Towed Vehicle,” and incorporated in its entirety by this reference.

FIELD OF THE INVENTION

The inventive supplemental braking device is a remote braking actuatorand a method of use of such a device from the field comprising safetydevices for towing a vehicle.

BACKGROUND OF THE INVENTION

To the avid recreational vehicle driver, having available a smallervehicle to use after reaching a campsite proves to be useful. Forexample, it is far easier to park a smaller vehicle in the parking lotoutside of a grocery store than a full-sized recreational vehicle. Thetowing of a smaller vehicle has become a part of the recreationalvehicle such that the towed vehicle is regularly referred to as a“dinghy” analogizing the operation of a recreational vehicle to pilotinga boat. A dinghy eliminates the need to break camp and stow everythingeach time the driver needs (or wants) to venture away from thecampground. Additionally, the dinghy can stow gear securely whenrecreational vehicle storage is filled (within weight restrictions), andthere is the sense of security engendered by having a spare vehicle forimmediate transportation in the event of an emergency, such as an injuryrequiring attention at a local emergency room.

Nonetheless, despite the acknowledged utility of towing a towed vehicleor “dinghy”, there are also acknowledged difficulties. One arrangementto facilitate towing is use of the simple tow bar where all four of thetowed vehicle's wheels will rotate in contact with the surface of theroadway (as opposed to using a dolly or trailer to support two or fourof the wheels respectively). Among recreational vehicle owners, thisarrangement is known as flat lowing, or four-wheels-down towing andemploys a tow bar between the towed and towing vehicles. Importantly, inusing a tow bar to pull the towed vehicle, the recreational vehicle mustthen both accelerate and decelerate a mass that is greater byapproximately one sixth of the recreational vehicle's own mass. Whilebeefing up the engine in the recreational vehicle can usuallyappropriately address the acceleration of the combined mass of the twovehicles, stopping that combined mass presents another issue.

Even if the braking capacity of the recreational vehicle is sufficientto slow the combined mass of the recreational vehicle and the towedvehicle, when the only braking is that applied by the towing vehicle,the stopping distance from any given speed will be lengthenedsignificantly. The momentum the towed vehicle contributes much more massthat must also be slowed along with the towing vehicle. When compared tostopping without the towed vehicle, decelerating that additional masssimply requires more braking force to slow the vehicles.

A solution readily asserts itself: each of the towing and towed vehicleshave braking systems sufficient to safely stop those vehicles when usedas separate vehicles. If both vehicles could suitably brake its own masswith its own braking system, the composite train of towing and towedvehicles can be slowed efficiently. Many recreational vehicle driverselect to implement the towed vehicle's own braking mechanism by means ofremote activation to enhance the braking action of the vehicles whenused together. Generally termed “supplemental braking mechanisms,” thesesystems include instrumentation used to activate the towed vehicle'sbraking system in concert with that of the to wing vehicle. In applyingthe supplemental braking, the total necessary force to decelerate thecombined mass of the recreational vehicle and the towed vehicle isspread across the eight or more wheels the two vehicles comprise,thereby allowing each wheel to slow the vehicles rather than merely thefour or so the towing vehicle controls.

In rough cut, this solution should work but the problem is in applyingthe brakes appropriately in the towed vehicle. Nonetheless, the need forstopping each of the towed and towing vehicles is universallyrecognized. For example, in executing panicked stops, the need forsupplemental braking is clearly demonstrated. Without supplementalbraking, stopping distances are simply too long to avoid collision orcatastrophe, and such stops are the leading cause of towing vehiclebraking system failure. So recognized is this danger that nearly everystate and Canadian province requires a supplemental braking system onall towed vehicles over a certain weight, in the same way that theyrequire brakes on trailers of a certain weight.

The tort system too recognizes the efficacy of supplemental braking.Because of the increased stopping distances when towing a vehiclewithout supplemental braking, accidents that could have been avoidedstill occur. In civil actions for negligence, if an accident that couldhave been avoided within the bounds of the towing vehicle's regularstopping distance occurs due to the added mass of the towed vehicle, adriver is much more likely to be found liable. The lack of asupplemental braking system is, as in failing to maintain a brakingsystem in proper working order, a distinct act of negligence resultingin liability due to causation.

Several types of supplemental braking systems exist within the priorart. The most basic type of supplemental braking system is a portable,electric brake controller that applies the towed vehicle brakes at afixed pressure over a duration defined by a voltage applied to thetowing vehicle brake lights as received from the brake light switch inthe towing vehicle. These systems act using relays to trigger brake “on”in the towed vehicle. The towed vehicle is either in a braked orfreewheeling state based upon the voltage at the brake light. A brakelight is either on or off and thus these prior art brake systems canonly apply a single selected pressure on the towed vehicle's brakes whenactivated. This two-state system lacks the ability to exert a pressureproportionate to that applied in the recreational vehicle.

Just as with the brake lights that trigger it, the system is either “on”or “off” with no degrees of application. For that reason, theapplication of brakes in the towed vehicle is very uneven and onlyroughly matched to that in the towing vehicle. More sophisticatedversions of the systems have an ability to predesignate a selectedamount of pressure to apply to the towed vehicle braking system inresponse to the signal from the towing vehicle. Rather than simplyapplying a maximum pressure to the brake system, these systems applypressure at a fixed pressure predesignated as, for example, “light”,“medium” or “heavy”. Trial and error allow a technician to “tune” thetowed and towing vehicle train to select what proves, in practice, to bethe smoothest of the designations available for this setting. Even when“tuned” in this fashion, the application of the brakes in the towedvehicle are not always optimal. For example, in light braking of thetowing vehicle, the dinghy applies the preset pressure and acts as ananchor; in heavy braking, by contrast, the preset pressure might notsupply enough braking force and the dinghy pushes the towing vehicle.Either option tends to lengthen stopping distances from what is optimal.Nonetheless, the stopping distances are far shorter than those producedby a system without supplemental braking. For that reason and the lackof expense, simplicity and reliability of these systems make thempopular among RV enthusiasts.

A second system which seeks to achieve a closer to optimal brakingdistance is known as a proportionate braking system. Rather than asingle pre-selected braking force, the proportionate system works byapplying a braking force in proportion to deceleration experienced bythe towed vehicle. Most proportionate systems exploit an inertial sensorsuch as a pendulum or accelerometer (such as a MEMS sensor implementedin an integrated circuit chip) to select a braking force in an intensityproportionate to the deceleration measured from a mounting point in thetowing vehicle.

Because in this second system, the degree of braking is based uponsensed deceleration experience in the towing vehicle, in the case ofhard deceleration, picking a proper relationship between senseddeceleration and applied braking in the towed vehicle dictates howclosely the system approaches optimal braking. The ratio between senseddeceleration and degree of braking force applied in the towed vehicle isexpressed as a coefficient. Selection of a suitable coefficient isnecessary for belter braking. For example, should the proportion ofapplied braking force relative to experienced deceleration be set toapply too great a pressure, the braking of the towed vehicle will dragthe towing vehicle causing it to experience a further deceleration or,at the extreme, to simply lock up the brakes of the towed vehiclecausing it to skid and drive the towing vehicle forward. At very least,this has the highly undesirable effect of wearing the towed vehiclebrakes unduly while not shortening stopping distances. When properlyadjusted, however, the system can approximate braking ranging fromheavy-duty emergency braking, to general everyday braking and, in theextreme, slow-to-an-idle braking. Unfortunately, because the system isbased upon the experienced and measured deceleration, there is a latencyin the system, i.e. a delay between the onset of braking in the towingvehicle and the application of brakes in the towed vehicle, the vehiclesdo not brake in a synchronized manner. The differences in brakeapplication tend to exert larger than necessary forces at the connectionbetween the two vehicles and unevenly wear the brakes as between the twovehicles.

A third class of supplemental braking systems is known as “direct”because they use the towing system braking fluid to move a piston in acylinder which, in turn depresses the towed vehicle brake pedal, just asthat fluid is also used to close a brake caliper. Direct systems requirea much more comprehensive installation process than most other systems,but they deliver superior braking. Like basic proportional systems,direct systems offer a whole spectrum of brake application intensitiesfrom emergency braking to slow-to-an-idle braking action; yet they havea far better response time and require little or no manual adjustment.Direct systems tap into the towing vehicle's brake lines using fluid(either air or hydraulic fluid) to move a piston in an actuator whichoperates similarly to the calipers on a brake. The actuator, in turn,applies a force on the fluid of the towed vehicle's brake system tosense the pedal movement in the towing vehicle so that the actuator inthe dinghy can replicate that same timing and pressure in the towedvehicle. Essentially, a direct system acts as an additional circuit inthe towing vehicle, such that brake pressure in either an air orhydraulic system in the towing vehicle drives a piston in a cylinder tosimilarly assert a pressure in the towed vehicle's system as would afoot on the brake pedal.

As stated above, because such a system functions as an extension of thebrake system of the towing vehicle, installation and removal of thesystem tends to be a very elaborate task. Also, because the entiresystem must apply both vehicle's brakes, the necessary pedal travel inthe towing vehicle lengthen and braking response tends to be “slushy.”Further, the actuators that link the systems must be very specificallyengineered for the two vehicles such that pedal travel asserted by theactuator on the towed vehicle's brake pedal achieves the same slowingeffect on the towed vehicle as the driver's foot asserts in the towingvehicle. These units tend to be very expensive because of the nearlycustom nature of the installation.

What is needed in the art is a system that does not require elaborateinstallation and can be readily switched from a towed configuration toan operating configuration for ready use of the towed vehicle as adinghy. Inherent or nontechnical synchronization of the asserted brakingforce to that experienced in the towing vehicle is necessary for safeoperation.

SUMMARY OF THE INVENTION

A system and method for braking a flat-towed vehicle based upon abraking pressure of a braking fluid in a braking circuit in the towingvehicle, the method includes measuring a piezoresistor voltage dropacross a piezoresistor positioned within the braking circuit such thatthe piezoresistor voltage drop changes in response to the brakingpressure within the braking circuit. Based upon the measuredpiezoresistor voltage drop, a motor frame duration is retrieved. Aclutch engages the motor output shaft to initiate a clutch frame. Uponexpiration of a programmed clutch delay, a motor frame initiates bysupplying power to a motor. Upon expiration of the motor frame duration,power to the motor is interrupted. The clutch continues to be engagedfor the duration of the clutch frame. The clutch releases allowing acapstan attached to the clutch to spin freely relative to the motoroutput shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred and alternative examples of the present invention aredescribed in detail below regarding the following drawings:

FIG. 1 depicts a prior art hydraulic braking system;

FIG. 2 depicts a prior art air braking system;

FIG. 3 depicts a piezoresistor for mounting within a braking circuit ofa towing vehicle to sense a braking pressure of braking fluid containedtherein;

FIG. 4 is an exemplary block diagram depicting an inventive supplementalbraking system;

FIG. 5 is an exemplary block diagram depicting a motor capstan assemblyactivated by the inventive supplemental braking system in connectionwith braking system of the towed vehicle;

FIG. 6 is a timing diagram for a switching network the inventivesupplemental braking system comprises;

FIG. 7 is a flowchart depicting actions by a controller in the inventivesupplemental braking system;

FIG. 8 is an exemplary block diagram of a preferred embodiment of theinvention depicting a motor capstan assembly activated by the inventivesupplemental braking system in connection with braking system of thetowed vehicle and including a rotary encoder;

FIG. 9 is an exemplary block diagram depicting an inventive supplementalbraking system including a rotary encoder; and

FIG. 10 is a flowchart depicting actions by a controller in theinventive supplemental braking system including a control loop basedupon sensed rotary position of the capstan.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Before discussing the operation of the inventive system, an overview oftwo conventional and distinct braking systems generally employed intowing vehicles is appropriate. The first of these is the hydraulicsystem which is often found not only in the towing vehicle but also inthe towed vehicle or dinghy. Such a hydraulic system 10 is portrayed inFIG. 1. While shown with both disk brakes 13 k and drum brakes 13 m,this hydraulic system is typical of cars available in the 1980s andlater of a class that might be used for either towing or as a towedvehicle. Later vehicles exclusively employ disk brakes and earliervehicles, exclusively drums. In this system, the wheel is attached tothe dram. There are brake shoes which the system 10 uses to contacteither of a rotating drum 13 m or rotating disk 13 k either of which isfixedly attached to its corresponding wheel when a brake pedal 9 isdepressed by the driver. The shoes slow rotation by driving a lining onan outer surface of the brake shoe against either the rotating drum 13 mor the rotating disk 13 k thereby employing friction at the outersurface to stop the rotation.

Hydraulic brakes make use of hydraulic pressure to force brake shoesoutwards against the brake dram 13 m or to grasp the disk 13 k byemploying Pascal's law or the principle of transmission offluid-pressure. In fluid mechanics, pressure exerted anywhere in aconfined incompressible fluid is transmitted equally in all directionsthroughout the fluid such that the pressure variations (initialdifferences) remain the same. The law was established by Frenchmathematician Blaise Pascal and bears his name.

The brake pedal 9 exerts a pressure on the rod 9 r which propels apiston down a cylinder known as the master cylinder 17 c (shown as apart of the master cylinder assembly 17) exerting that pressure againsta volume of hydraulic fluid. The fluid pressure is conveyed from themaster cylinder 17 c through the hydraulic lines 18 h to either thecalipers 15 p or to each of the brake cylinders 15 n, in either caseurging the brake surfaces against either the drams 13 m or the rotors 13k. Clamping onto the drams 13 m or the rotors 13 k exerts the slowinginfluence upon each of the wheels in turn.

When the driver releases the brake pedal 9, the piston in the mastercylinder 17 c returns to its original position due to the pressure thereturn spring exerts. Thus, the pistons in the wheel cylinder come backin its original inward position. As the piston returns to its restposition, Pascal's Law exerts its converse result, the pressure in theindividual brake cylinders 15 n and brake calipers 15 p drops equallyreleasing the grip on each of the drums 13 m and the rotors 13 kreleasing the wheels to rotate freely. Reversing the movement of thecalipers when the brakes were applied, the drop in fluid pressure causesthe calipers to retract and the brakes are released.

As discussed above, a vacuum booster 17 b multiplies the pressureasserted on the hydraulic fluid to increase the efficiency of thebrakes. The vacuum booster 17 b was invented in 1927 to provide ashorter stopping distance with less effort. The booster 17 b works bypulling the air out of the booster chamber with a pump creating alow-pressure system relative to the ambient atmospheric pressure. Whenthe driver steps on the brake pedal, the input rod on the booster ispushed in which lets atmospheric pressure into the booster. This, inturn, pushes the diaphragm toward the master cylinder. The diaphragm,then, at sea level adds pressure to the piston across the surface ofabout 15 pounds per square inch, at sea level, across the diaphragm. Todo this, however, it is necessary to evacuate the chamber on theopposite side of the diaphragm, otherwise, the pressures being equal,there is no differential in pressure and no assistance upon applicationof pressure on the brake pedal. Generally, the intake manifold of arunning engine is used as a very good source of vacuum for this purpose.

FIG. 2 portrays an alternate embodiment of a prior art braking system isknown is commonly as an air brake system 12. The air brake system 12consists of a two-stage air-compressor 14 driven either by thecrankshaft or gearbox shaft. The compressor 14 takes air from ambientatmosphere, compresses it and delivers the compressed air to an airreservoir 11 v through un-loader valve or governor 11 g. Where thepressure within the reservoir 11 v reaches the maximum degree, theun-loader valve 11 g opens to the atmosphere. Then the compressed air isported to the atmosphere directly to maintain the pressure within thereservoir 11 v at a selected operating pressure.

Each of the four wheels fitted with brake chambers 15 s consists of adistinct diaphragm, and to which compressed air from the reservoir isapplied through a brake valve 17 v to apply a clamping force to thedrums 13 m and the rotors 13 k in a manner similar to that of thehydraulic brakes set forth above. Specifically, the diaphragm in eachbrake chamber 15 s exerts a force on a cam actuating lever (not shown)and applies the brake. Each of the brake chambers 15 s is connected tothe reservoir through a valve 17 v, itself responsive to a brake pedal.

When the brake pedal (not shown) is pushed the brake valve 17 v opensand compressed air can flow from the reservoir 11 v to the brake chamber15 s. The brake valve 17 v consists of three passages communicating,respectively to each of an:

-   1. Air intake;-   2. Exhaust; and-   3. a Brake chamber.    When the brake pedal is pressed, the exhaust passage will be closed    and the air intake passage open allowing the compressed air to go    back to the chamber 15 s. During a return stroke, the exhaust    passage opens while the air intake closes, and exhaust air is ported    to the atmosphere. This system is generally fitted with an emergency    mechanical brake, which can be used when air supply fails the air    brake system 12.

An air brake system 12 is used in heavy vehicles because air brakes canassert a greater frictional force than either hydraulic or mechanicalbrakes. Additionally, because the components except for the brake valve17 v and the rotors 13 k or drums 13 m, can be placed anywhere withinthe vehicle body, use of air brakes simplifies the chassis design.Finally, because the reservoir is generally sized with a sufficientmargin for exigencies, it can also supply compressed air for other needssuch as tire inflation, to activate a horn, to drive windscreen wipersand other such needs such as inflating a buffer to support a driver'sseat. Naturally, because the air brake system 12 relies upon thepresence of pressure within the reservoir 11 v, preventing, detecting,locating, and repairing leaks within the system is a critical task inmaintenance.

Having reviewed conventional braking systems present in either of towingvehicle systems, the discussion moves on to one of the primary elementsof an inventive supplemental braking system. Unlike conventional directsystems (as described above in the Background) which seek to employpressure in either of the hydraulic or compressed air lines tomechanically move a piston in an actuator, the inventive system relies,instead upon sensing pressure within a brake line without acorresponding movement of a piston increasing the necessary volume ofbraking fluid to actuate the brakes, be that fluid either air orhydraulic fluid. A purely mechanical connection such as that used in adirect system as described above, draws off a significant volume ofhydraulic fluid as the piston is motivated down the cylinder of theactuator.

To sense fluid pressure in either of the above-described hydraulic(FIG. 1) or air (FIG. 2) braking systems, the inventive system employs apiezoresistive silicon devices which measures the stress detected in asemiconductor as exerted by the braking fluid. As shown in FIG. 3, apressure sensor 30, in its preferred embodiment is a piezoresistivesilicon device installed as a fitting within either of a hydraulic line18 h (FIG. 1) or an air braking line 18 a (FIG. 2) contain a brakingfluid (air or hydraulic fluid) 18 f. As shown, the sensor includes afitting body 30 f (either brazed or threaded into the line 18 h).Electrical conductors 30 c pass through a sensor housing 30 h mounted onthe fitting 30 f. These conductors 30 c are generally potted in an inertsubstance 30 p such as, for example, epoxy. A piezoresistivesemiconductor 30 p is mounted at the base of the fitting in contact witha plate 30 d. In a preferred embodiment, a protective screen 30 s ismounted to allow pressure to reach the diaphragm plate 30 d withoutallowing debris to collect within a cavity defined by the interspacebetween the screen 30 s and the diaphragm plate 30 d.

The piezoresistive effect involves pressure or stress. In apiezoresistive pressure sensor, a piezoresistor is usually implanted inthe surface of a thin silicon diaphragm. To understand the effect,imagine the piezoresistive semiconductor 30 p as a portion of a skin ofa balloon. As greater pressure is applied to that skin to inflate theballoon, the matrix of the semiconductor 30 p is stretched and theresulting strain impacts the carrier mobility and number density.Because electrons that travel these paths must travel further with fewercarriers per unit volume, the resistance of the semiconductor rises asthe strain increases. Thus, by knowing the relationship between thepressure acting on the diaphragm plate 30 d and the resulting resistancebetween the electrical conductors 30 c, a measured resistance can resultin a derived pressure within the lines.

In most instrumentation applications, semiconductors generate either apotential or voltage between two conductors 30 c. Such a measured chargeor voltage is relatively easy to employ in a sensor. In the case ofpiezoresistive semiconductors 30 p, however, changes in resistanceacross the piezo material is the product, and can only be measured as acurrent change while a reference voltage is placed across the twoconductors 30 c, i.e. Ohm's law. The current in a circuit is directlyproportional to the electric potential difference impressed across itsends and inversely proportional to the total resistance offered by theexternal circuit. Thus, to measure pressure applied across a surface ofthe piezoresistive semiconductor 30 p, one must measure a change in thecurrent through the piezoresistive semiconductor 30 p due to a change inelectrical resistance.

Valued for their high sensitivity and linearity, piezoresistive pressuresensors were some of the first MEMS devices to come to market. Variousindustries implement these devices in their products to measurepressure. For example, the biomedical field uses piezoresistive sensorsas tools to measure blood pressure, while the automotive industry usesthem to gauge oil and gas levels in car engines. These industries favorthe use of piezoresistive sensors 30 because of the ability to measurepressure over a wide range without any resulting change in volume of thesystem being measured. The insignificant volume change is possiblebecause such deformation of the piezoresistive semiconductor 30 p due topressure is insignificant when compared to the operating volume.

Using a piezoresistive pressure sensor 30 assures that the observereffect is minimized. In science, the term “observer effect” refers tochanges that the act of observation will make upon the phenomenon beingobserved. This is often the result of instruments that, by necessity,alter the state of what they measure in some manner. A commonplaceexample is checking the pressure in an automobile tire; this isdifficult to do without letting out some of the air, thus changing thepressure. This effect can be observed in many domains of physics and canoften be reduced to insignificance by using better instruments orobservation techniques. In this case, the deformation of thepiezoresistive semiconductor 30 p requires only the very slightestchange in the volume of the towing vehicle's brake system and thus,monitoring the pressure in the towing vehicle's braking system has aninfinitesimal effect on the towing vehicle braking efficiency.

FIG. 4 portrays the electronic and electrical system employed in thepreferred embodiment of the invention. Shown are both hydraulic fluid 18h in the line and the pressure sensor 30. The pressure sensor 30 in itspiezoresistive embodiment exists in the system 20 as a variableresistor. A resistor has no polarity and will present the sameresistance to current flowing in either direction. The resistance is thesame regardless of the orientation of the probes across it. For thatreason, the conductors 30 c (FIG. 3) are defined as the negativeterminal (low potential) or the positive (high potential) terminal asplaced the circuit which comprises the pressure sensor 30,

The preferred embodiment of the supplemental braking system 20 isdesigned to be powered from a 12-volt DC source. Nearly all modernautomobiles have a 12-volt DC electrical system and, in the preferredembodiment, the system is powered by the electrical system of either ofthe towed or the towing vehicle, in most instances, the towing vehicle.A voltage regulator within the vehicle supplying that voltage regulatesthe charging voltage that an alternator the vehicle's engine drivesproduces. Generally, the voltage regulator keeps the vehicle voltagebetween 13.5 and 14.5 volts to protect the electrical componentsthroughout the vehicle. A second voltage regulator is interposed betweenthe vehicle electrical system and the supplemental braking system 20 tocondition the output as a power source for computer logic. The output ofthe second voltage regulator is shown as a DC source 50.

Extending from the ground side of the DC source 50, the circuit includesa ground provided to each of a breakaway switch 52, a control board 40,a gearhead motor 60 and an electric clutch 62. The positive side of theDC source 50 is connected to a master switch 56. In its closed position,the master switch 56 provides potential and current to the whole of thesystem 20. The system 20 includes, as well, the pressure sensor 30, thecontrol board 40, the gearhead motor 60 and the electric clutch 62 eachreceiving power from the DC source 50.

A gearhead motor is an electric motor that includes a reduction gearcluster or gearhead to drive an output shaft. The gearhead was mainlyused to change the motor speed and as a torque amplifier. With theintroduction of motors incorporating speed control functions, theprimary role of the gearhead is to amplify torque. The gearhead inembodiments of the invention also the torque necessary to drive themotor backwards. The gearhead motor functions as a “one-way” rotationaldevice.

Throughout this teaching, there exists a mechanical connection betweenthe gearhead motor and the towed vehicle brake pedal which will bereferred to as a “cable.” The term “cable” as used here is moreinclusive than in its standard definition, i.e. “a thick rope of wire ornonmetallic fiber, typically used for construction, mooring ships, andtowing vehicles,” As used herein, it would also include the broaderdefinition “a band of tough flexible material for transmitting motionand power” and would include, for example, a molded and flexibleNylon(tm) tie rod or any linkage effective to draw down the brake pedalactuating the brake. In a preferred embodiment, the “cable” refers to aflexible nylon rack that is retracted by rotation of a pinion gearaffixed to the output shaft of the gearhead motor.

The control board 40 drives each of the gearhead motor 60 and theelectric clutch 62 and traces to each are shown exiting from contacts onthe right-hand side of the symbol representing the control board 40 inFIG. 4. In an alternate embodiment, relays might be used. Relays areused in electrical circuits to isolate and protect logical circuits fromhigh current draw which might burn smaller conductive paths. Instead, arelay will, when activated, act as a closed switch allowing current toflow in a second circuit. Relays used as electronic controls or inswitching circuits either may be mounted directly onto PCB boards suchas the control board 40 or connected as free standing devices. Relaysare selected according to the current they are to accommodate on theswitched side which load currents are normally expressed in valuesranging from fractions of an ampere up to 20+ amperes. While simplifiedin this diagram, prudent design will generally prevent large currentvolumes from passing through the control board 40 and it is the intentof the inventor that this instant description will include any suchprudent designs. The rudiments of each are adequately portrayed in thisFIG. 4 such that the operation of the inventive device can beunderstood. Also, while relays are described herein, the presentlypreferred embodiment accommodates this function with solid stateswitching devices having equivalent capacities.

The control board receives two input signals. The first such signal isfrom the pressure sensor 30, and the other signal is from a normallyopen contact switch, the breakaway switch 52. These two input signalsare used to drive each of the gearhead motor 60 and the electric clutch62 in two different modes of operation as is listed below.

The easier of the two modes to understand is that known as the“breakaway mode”. State laws vary, but some states require a stoppingability within a specified distance from a stated speed, and manyrequire a “break-away” brake for situations where in response to thetowed vehicle becoming unhitched, the towed vehicle will brake to slowat its practical maximum rate to prevent run away of the towed vehicle.At 49 CFR § 393.43 entitled “Breakaway and emergency braking”, the Codeof Federal Regulations states “(a) Towing vehicle protection system.Every motor vehicle, if used to tow a trailer equipped with brakes,shall be equipped with a means, in the case of a breakaway of thetrailer, to activate the service brakes on the towing vehicle andstopping the towing vehicle.”

The normally open contact switch 52, then, is like a dead man's switch.In a preferred embodiment of the breakaway switch 52 is the Tekonsha™described as a “[c]ompletely sealed breakaway switches to automaticallyset trailer brakes in case of accidental trailer breakaway,” TheTekonsha™ switch comprises two contacts urged together by spring mounts.A wire rope extending from the towed vehicle terminates in a strip ofinsulating material that is interposed between the contacts. As such,the contacts are held apart so long as the strip is between them. Whenthe strip is removed by the movement of the towed vehicle away from thetowing vehicle, the contacts connect completing a circuit. The flow ofcurrent through the switch sends a signal indicative of a “breakaway.”

In a second embodiment, a wire rope extending from the towing vehicle tothe towed vehicle terminates in a strong magnet, for example, aneodymium magnet. The breakaway switch 52, in this preferred embodimentis a magnetic reed switch which closes under the influence of themagnetic field surrounding the neodymium magnet. Therefore, using aferrous plate on the front of the towed vehicle to support the normallyopen contact breakaway switch 52, the cable can readily be affixed sothat in normal towing the switch remains closed and the control board 40senses a closed circuit enabling normal operation. Should the towedvehicle separate from the towing vehicle, presumptively the cable willpart at the plate with the magnet remaining affixed to the cable andthus to the towing vehicle. Removing the magnet allows the switch toopen and the control board senses the fault as indicative of a“breakaway.”

In either embodiment, upon sensing a “breakaway,” the control board thenapplies the brakes in the towed vehicle in accord using the clutch 62and the motor 60 as described below. Thus, the inventive system complieswith regulatory and prudential requirements, bringing the towed vehicleto a complete stop in the event of a breakaway. In the preferredembodiment, a “shortest stopping distance” of towed vehicle brakeapplication sequence is known to the controller or stored in nonvolatilememory therein and applied in any instance of “breakaway.”

The second mode is the operating state or mode. While in operating mode(any time that the breakaway switch is in its operating as opposed to“breakaway” mode) the braking of the towing vehicle determines thebehavior of the towed vehicle. Naturally, if a supplemental brakingsystem applies too little braking relative to the braking applied by thetowing vehicle, the towed vehicle wants to overran the towing vehiclecausing undue brake pad wear on the towing vehicle. If, on the otherhand, the towed vehicle applies more braking than would be appropriatefor the towing vehicle, the towed vehicle acts as an anchor or drogueand the excess friction unduly wears the brake pads of the towedvehicle. It is the objective, then, of any supplemental braking system,to provide an exact amount of braking on the towed vehicle to reflectthe braking applied at the driver's behest in the towing vehicle. Ineach case, applying brakes at a selected pressure for a selectedduration in the towing vehicle ought to result in a specific brakingapplication in the towed vehicle.

In the prior art, the relationship between the application of brakes inthe towed vehicle is a mechanical function derived from one of threepossible inputs:

-   -   1) Mechanical movement of a piston in the towing vehicle's        braking system;    -   2) Sensed acceleration (accelerometers, pendulums, etc.) in the        towing vehicle; and    -   3) Surge-type braking based upon extension and compaction of a        towing yoke,

Each of these systems uses a relatively linear response curve to applybrakes at the pedal of the towed vehicle in rough proportion to movementof a sensing device, for example, a pendulum in an accelerometer or apiston in a proportionate system. While never perfect at the balancebetween towing braking and towed braking, each system has could roughlyapproximate an appropriate balance between a towed and towing vehicle.Advantageously, the instant system 20 can be more appropriatelyconfigured to optimally brake the towed vehicle assuring better controland much less wear on either of the towed or towing vehicle brakingsystems.

Because the selected response to each sensed pressure in the towedvehicle system, can be optimally selected, i.e. selected to address thedecelerative state of the towing vehicle, a perfect balance of brakingbetween the two vehicles is always struck. In one embodiment of thesystem, there is a simple coefficient stored that relates brakingperformance in the towed vehicle to sense fluid pressure in the towingvehicle. In many cases this is a very useful embodiment.

In a simplest embodiment of the braking system, braking characteristicsof the towed vehicle are known and a single coefficient is appropriateto select a braking pressure used in response to a sensed pressure inthe towing vehicle brake lines at the pressure sensor 30 and theresponse or responses to that sensed pressure are “hard coded” intosoftware or firmware to dictate how the motor 60 will respond to thatsensed pressure. In such an embodiment, the response is linear, which isto say that the braking pressure exerted on the brake pedal isproportionate to the sensed pressure.

In another embodiment, each increment of sensed pressure is associatedwith a coefficient stored in the system and that coefficient is used todetermine the cable travel the system will implement in response to thatsensed pressure. No linear or even curvilinear construct binds thisembodiment of the system. A look-up table informs each response to anysensed pressure at the pressure sensor 30.

In computer science, a lookup table is an array that replaces runtimecomputation with a simpler array indexing operation, i.e. rather than tocalculate a value based upon sensed pressure at the pressure sensor 30,the system 20 simply recalls a previously selected value. The savings interms of processing time can be significant, since retrieving a valuefrom memory is often faster than undergoing an “expensive” computationor input/output operation. The tables may be precalculated and stored instatic program storage, calculated (or “pre-fetched”) as part of aprogram's initialization phase (memoization—in computing, memoization isan optimization technique used primarily to speed up computer programsby storing the results of expensive function calls and returning thecached result when the same inputs occur again.), or even stored inhardware in application-specific platforms. Lookup tables are also usedextensively to validate input values by matching against a list of valid(or invalid) items in an array and, in some programming languages, mayinclude pointer functions (or offsets to labels) to process the matchinginput.

In a further embodiment, the braking of the towed vehicle benefits froma vacuum assist or power-assist braking function in the towed vehicle.When the dinghy or towed vehicle is in normal operation, the engine,while running, draws large volumes of air into its cylinders to supplyoxygen to the combustion of fuel therein. A port near the intake usesthat movement of air into the engine to induce a vacuum which can bestored in a vacuum reservoir, essentially an empty air-tight chamber.The reservoir is used to evacuate a chamber on one side of a diaphragm.On the opposite side of the diaphragm, a progressive valve admitsatmospheric pressure in proportion to the movement of the brake pedalthereby multiplying the pressure exerted to move a piston in the mastercylinder to apply a braking force at the wheels.

Typically, without the engine running, there is no vacuum to evacuatethe chamber on the one side of the diaphragm relative to atmosphericpressure. Thus, the power-assist feature does not function when thetowed vehicle's engine is off. An active braking system taps into aseparate vacuum source to supply the vacuum used to evacuate the chamberon the sealed side of the diaphragm. The supplied vacuum enables thepower-assisted braking capability in the dinghy just as though theengine were running. Using either of the towing vehicle's own generatedvacuum or an electric vacuum pump to supply a vacuum enables thepower-assist braking function of the dinghy to function just as thoughits own engine was running.

Thus, in operation of the preferred embodiment, with the breakawayswitch 52 in its operational state and the master switch 56 in a closedstate, the sensed pressure at the pressure sensor 30 will evoke aspecific and selected response by application of brakes at the pedal ofthe towed vehicle for a specific duration and pressure designated withinthe look-up table. Pressure is applied to the brake pedal 9 (FIG. 5) ofthe towed vehicle in accord with the values retrieved from the look-uptable displacing the brake pedal 9 in a manner very like an operatordepressing that pedal 9. The control board 40 assures that depressing abrake pedal in the towing vehicle would increase the fluid 18 haccording to Pascal's law as described above. In response, the sensor 30will diminish a current flowing to the control board 40 in proportion tothe sensed pressure at the sensor 30. Sensing the diminution of current,the control board looks up a response dictated based upon the sensedpressure. Then signals are sent to each of the motor and the clutch, inturn, in accord with the looked-up response.

The control board 40 controls the electric motor 60 and clutch 62 inapplying pressure to the brake pedal 9 in operation. In the preferredembodiment, the pressure range of the sensor is user-selectable to allowfor use on either of a hydraulic or air-based braking system. Tofacilitate this user-selectable operation, the control board 40optionally includes either of a hardware or software means to switch thescale of input from the pressure sensor 30, to select ranges of, forexample, from 0 to 125 psi or 0 to 3000 psi as an operating range. Oncea range is set, the values retrieved will be appropriate for the brakingmeans of the towing vehicle. The clutch 62 and motor 60 will receivesignals based upon the sensed pressure and the type of braking system ofthe towing vehicle.

Generally, the values that a manufacturer might designate in the look-uptable are within a range that will provide superior results to othersystems independent of the knowledge as to the make and model of each ofthe towing and towed vehicles. Vehicles selected as a “dinghy” fallwithin a weight group and might have similar braking characteristics. AFord Escape™, Subaru Forester™, Honda CRV™ and a Toyota RAV4 may notdiffer so much in their braking characteristics such that distinctvalues are necessary to approximate optimal braking results. In at leastone embodiment, families of “dinghies” having similar weight, weightdistribution, and braking performance might be represented by a singleset of values.

In another embodiment, the selected values are merely starting points aselements of a dynamic look-up table. In one further embodiment,accelerometers are placed in each of the to wing and towed vehicles todetermine the deceleration of each upon braking. Using an iterativeapplication of artificial intelligence, these values can be refined toachieve maximum braking effect at each of the wheels of both towed andtowing vehicles. Indeed, in such an embodiment, the accelerometers mightinclude x- and y-axis measurements to allow for distinct values forstraight-line braking and for braking to either of the left or rightdirections. Markov decision processes provide a useful framework forsolving for optimal braking by applying sequential decision making underuncertainty. Relative to some Important environment variables, i.e.state of the road surface and condition of the tires, decisions onpartial information about the system state. Thus, a dynamic lookup tableis populated on an iterative basis using the more general framework ofpartially observable Markov decision processes. By changing thecoefficients and observing the sensed deceleration at the sensors, acontroller can iteratively “zero in” on optimal values with which itwill populate the dynamic lookup table. However, having a dynamiclook-up table is not essential to the invention and in most instances ofthe invention, the values for braking will be designated at the time ofsale to remain static in use.

In a further embodiment of the braking system, the Markov decisionprocesses are further informed by a set of temperature sensors locatedat the calipers of the brakes in the towed vehicle. Since brake heatenergy is only related to the amount of kinetic energy being converted,it doesn't matter whether the brakes are applied hard for a short timeor light for a long time, the resulting heat will be the same if thedesired speed reduction is the same. If all the brakes on a vehicle aregenerating the same amount of brake torque, the heat created byconverting kinetic energy will be evenly distributed through all thebrakes. However, imbalance caused by poor maintenance, poor loaddistribution, or light brake applications may cause an unevendistribution of brake heat with some brakes possibly overheating. Thetypical generic “normal driving” temperature range for well-balancedvehicle brakes is 100 to 200 degrees. A controlled mountain gradedescent can produce brake temperatures between 200 and 400 degrees.

Brake system heat is dissipated through radiation, conduction, andconvection due to a temperature gradient. Radiation is the transfer ofheat through space. Conduction is the transfer of heat to parts of thebrake system and other attached vehicle parts. Convection is thetransfer of heat from the brake to the air moving across the brake.Because of the limits on how quickly heat energy can be dissipatedthrough radiation, conduction, and convection, a brake system cansometimes build up heat faster than it can be removed. This imbalancebetween the heat coming into the system and the heat leaving the systemis referred to as saturation. If this imbalance persists and thesystem's heat builds up to certain temperature thresholds, then brakefade can occur. The temperature thresholds for brake fade vary dependingon the brake system and the category of the fade experienced.Nonetheless, the brake performance of the towed vehicle can be furtheroptimized in a dynamic lookup table by Markov decision processesobserving each of acceleration and temperature to achieve optimumbraking towed vehicle relative to the towing vehicle.

In a further embodiment, these same sensors can trigger any of a light,warning sound or both or to drive a gauge to inform the driver as totemperature and its concurrent effect upon braking efficiency. Just aswith coolant temperature, it is extremely advantageous to supplyinformation to the driver of the towed vehicle. Where extremetemperatures are detected, a signal might indicate the need for thedrive of the towed vehicle to stop and inspect the towed vehicle for anindicated malfunction of the towed vehicle braking system.

In FIG. 5, a simplified diagram of the mechanism for placing pressure onthe to wed vehicle's brake pedal 9 is shown. In the presently preferredembodiment, a pulley 63 p is attached to a floor pan of the towedvehicle while the motor 60 (FIG. 4) is placed at a fixed point such ason the floor pan at a forward edge of a driver's seat. A cable 64terminates at a clevis 65 attached to the brake pedal 9. (For thepurposes of this explanation, the term cable is used. As expressedabove, it is the inventor's intent that what is expressed as cableherein includes any relatively long narrow strip of pliant materialmight be used. Therefore, what this specification labels as cable mightbe a chain, a metal ribbon such as that of a mainspring, a webbing strapsuch as of Nylon™, or a polyester webbing strap, a wire-rope, a Kevlar™line, or any such similar structure including, as expressed above aNylon™ toothed rack mating with a toothed capstan 68. Importantly, whenthe inventor uses the term “cable” that structure is not merely alimited to a wire rope.) From the pedal 9, the cable 64 passes over apulley 63 p sheave (held to the floor pan by a sheave cheek stanchion 63s) and onto a reel of a capstan 68 which, alternately, pays out andtakes up the cable 64. When the capstan 68 takes up the cable 64 windingit about the reel, the movement of the cable 64 acts to draw the pedal 9downward, thereby engaging the brakes in the towed vehicle. When thecapstan 68 is allowed to freewheel, the pressure exerted by the returnspring pulls the pedal 9 back up to its full pedal height drawing thecable 64 back through the pulley 63 p causing the capstan 68 to pay outthe cable 64 to an “at rest” position.

To cause the capstan 68 to take up the cable 64, an electric motor (notshown, 60 in FIG. 4) is used. Because, in the preferred embodiment areduction such as the worm screw 60 w and worm wheel 60 g arrangementsuch as that shown, is used to greatly increase the torque turning thecapstan 68, the worm wheel 60 g only spins with input from the motorinput shaft. Unlike ordinary gear trains, the direction of transmission(input shaft vs output shaft) is not reversible when using largereduction ratios. Due to the greater friction involved between the wormscrew 60 w and worm-wheel 60 g, especially when usually a single start(one spiral) worm, there is a ratcheting effect when the motor 60 (inFIG. 4) applies torque to the capstan 68. This can be an ad vantage whenit is desired to eliminate any possibility of the output driving theinput. Something is needed to decouple the capstan 68 from the wormwheel 60 g to enable the pay out of the cable 64.

In the preferred embodiment, an electromagnetic clutch 62 (FIG. 4) isinterposed to allow the capstan 68 to freewheel paying out the cable 64.Electromagnetic clutches operate electrically but transmit torquemechanically. Therefore, they used to be referred to aselectro-mechanical clutches. When the control board 40 (FIG. 4) sends acurrent to actuate the clutch 68, that current flows through theelectromagnet producing a magnetic field. A rotor portion of the clutchattached to the capstan 68 becomes magnetized and sets up a magneticloop that attracts an armature attached to the worm wheel 60 g. Thearmature is pulled against the rotor and a frictional force is generatedwhere they contact thereby locking the capstan 68 to the worm wheel 60g. Within a relatively short time, the capstan 68 is accelerated tomatch the speed of the worm wheel 60 g. If the motor 60 is spinning,engagement of the clutch 62 will cause the capstan 68 to take up cable64 drawing the brake pedal 9 through its pedal height toward the floorpan. When the clutch 62 (FIG. 4) stops receiving the current from thecontrol board 40, the capstan 68 is tree to rotate and the force thereturn spring 69 exerts draws the cable 64 back off of the capstan 68 toan “at rest” position. In this manner, the system 20 (FIG. 4) canactivate and release the brakes in the towed vehicle.

It is important here to point out that apart from the exploitation of acable to draw the pedal down, there is nothing about this configurationof pulley 63 p and cable 64 that is necessary to effect the ends of theinvention. Alternate embodiments include the mounting of the motor 60,clutch 62 and capstan 68 on the floor pan itself to draw the pedaldownward without the use of a pulley 63 p. In FIG. 5, the alternateembodiment would place the capstan 68 and worm wheel 60 g where thepulley 30 p and the stanchion 63 s are shown.

Still another embodiment would obviate the pulley 63 p by use a Bowdencable and fixture point, placing the motor remotely. A Bowden cable is atype of flexible cable used to transmit mechanical force or energy bythe movement of an inner cable relative to a hollow outer cable housing.The housing is generally of composite construction, consisting of aninner lining, a longitudinally incompressible layer such as a helicalwinding or a sheaf of steel wire, and a protective outer covering.Examples of such Bowden cables are as used for gear shift cables onbicycles and throttle cables on motorcycles. Usually provision is madefor adjusting the cable tension using an inline hollow bolt (oftencalled a “barrel adjuster”), which lengthens or shortens the cablehousing relative to a fixed anchor point. Lengthening the housing(turning the barrel adjuster out) tightens the cable; shortening thehousing (turning the barrel adjuster in) loosens the cable.

Thus, by placing the fixed anchor point at the pulley stanchion 63 s,the motor 60, clutch 62 and capstan 68 could draw down the brake pedal 9located remotely from fixed anchor point such as being mounted on theengine firewall. The only important aspect to the configuration of thecable 64 is that when the control board 40 sends current to the clutch62, such that the motor 60 drives the capstan 68 for a calculated timeframe to effect the longitudinal translation of the cable 64 drawing thepedal 9 downward through its pedal height causing the towed vehicle tobrake.

Thus far, it is understood that the control board 40 exploits a pressuresensor 30 to sense pressure in the towing vehicle brake lines such thatupon application of the brakes in the towing vehicle, the control board40 sends a current to the clutch 62 and to the motor 60 causing thecapstan 68 to take up cable 64 drawing down the brake pedal 9 therebyapplying brakes of the towed vehicle. The actual working of the controlboard 40 is where the advantages of the instant invention makethemselves evident.

The control board 40 drives the motor 60. In the preferred embodiment,this motor is a direct current, permanent magnet, brushed electricmotor, which has a reputation as the workhorse of small, poweredmechanical systems. The presently preferred embodiment the motor 60 isone of a type referred to as a “gearmotor” because coupled to an outputshaft of the motor 60 is a transmission or “gearhead.” In the case ofthe preferred embodiment the gearhead comprises the worm screw 60 w andthe worm wheel 60 g portrayed in FIG. 5. Small motors like to spin fastwith low torque. The gearing reduces the shaft speed and increases thetorque. The four essential facts that dictate the basic properties of aDC motor:

-   -   1) For a fixed load, the shaft speed is proportional to the        applied voltage;    -   2) For a fixed voltage, the shaft speed is proportional to the        torque load applied to the shaft;    -   3) The shaft torque is proportional to the applied current, no        matter what the voltage; and    -   4) There is internal electrical resistance and internal        mechanical friction.

The motor speed when nothing is impeding rotation of the shaft is calledthe no-load speed. When a load stops the shaft from turning, such acondition is called “stall”. At stall, the amount of torque available iscalled stall torque. Motors have torque-speed curves. For a fixed inputvoltage from a battery, the motor speed slows down as it is loaded. Withno load on the shaft (free-running), the motor runs at the no-load speed(NLS), the fastest possible speed for that voltage. When the shaft isfully loaded and not allowed to move, the speed is zero and the motor isproducing its stall torque (ST), the maximum possible torque. At stalltorque, the current drawn out of battery is at its maximum, as is motorheating. Ideally, motors should be operated at stall only for briefperiods of time (seconds) to save on batteries and to keep the motorfrom melting. The term “operating point” indicates the speed the motorwill run when driving a specific operating load. As that load changes,the operating point slides up and down the torque-speed curve. Becausethe torque is at its maximum at stall or zero speed, the clutch 62 canbe advantageously used to apply maximum torque to accelerate the capstan68.

FIG. 6 sets forth the two signals the control board 40 sends to themotor 60 (FIG. 4) and the clutch 62 (FIG. 4). The signals shown aresimply binary in nature and thus are square waves, i.e. on or off. Theduty cycle commences as the pressure sensor senses a pressure in thetowing vehicle braking system until, at the end of a configurable firstinterval 61 a, the clutch is engaged at a time 41 a shown here as theonset of a “1” on the clutch trace 40 c. Then, after a second interval61 b, at a time 41 b, the motor trace 40 m also advances to a “1” or“on” voltage. A third interval 61 c wherein the motor trace 40 m and theclutch trace 40 c is characterized by the rapid drawing in of the cablemoving the brake pedal (shown in FIG. 5) ends at a time 41 c where themotor trace 40 m drops to “0” shutting off the motor. During this time,the clutch trace 40 c continues in the “on” state, locking the movementof the cable in a tensioned state. The locked cable state persiststhrough the duration of a fourth interval 61 d terminating at a time 41d when the clutch trace 40 c goes to “off” or “zero”, disengaging theclutch 62 allowing the cable to ran free. Once the clutch 62 (FIG. 4)disengages at 41 e, the capstan 68 (FIG. 5) allows the cable 64 (FIG. 5)to pay back out releasing the pressure on the brake pedal 9 (FIG. 5). Assuch, such are the five events in a typical duty cycle: The onslaught ofpressure in the towing vehicle brake system at 41 a; the clutch isengaged at 41 b; the motor goes “on” at 41 c; the motor goes off at 41d; and the clutch disengaged at 41 e.

These five events define six system states of interest. The first ofthese states is defined by the configurable period of delay between thesensed onslaught of pressure at 41 a and the engagement of the clutch at41 b, the interval labeled in FIG. 6 as the “Programmed Brake Delay” 42.The Programmed Brake Delay 42 is a configurable interval between thesensed onslaught of pressure at 41 a and the lock up of the clutch at 41b. This Programmed Brake Delay 42 can be extended from a nearlyinstantaneous engagement of the clutch 62 (FIG. 4) to engagement severalmilliseconds later. Drivability of towed/towing vehicle train can oftenbe enhanced by a slight delay in the onset of braking in the towedvehicle. In a preferred embodiment of the instant invention, this valueis configurable and can be stored as an integer.

The clutch engages at 41 b commencing the Clutch Frame or ClutchEngagement Interval. In a preferred embodiment of the invention, thereis a configurable variable, the Program Clutch Engagement Time Delay 43.This variable is designated to define a duration of a delay wherein thecontrol board 40 waits (the delay selected to be expressed as an integerdefining a number of milliseconds) before activating the clutch at thetime 41 a. By delaying the activation of the clutch to a time 41 a, thepredictability of the behavior of the towing vehicle acting as a unitwith its entrained towed vehicle during light braking is improved. Theinterval wherein the clutch is engaged is termed the Clutch Frame 46 andextends, on each end beyond the interval when the motor is energized,i.e. the Motor Frame 46.

At the expiration of the Program Clutch Engagement Time Delay 43, theControl Board sends a signal, at time 41 c to apply a DC current to themotor to commence the Motor Frame 44. The duration of the Motor Frame 44is determined by a value retrieved from the lookup table correspondingto the sensed pressure value, as described above relative to the capstan68 taking up the cable 64.

When the Motor Frame expires at a time 41 d, the clutch remains engagedas shown by the Clutch Frame 46 beginning an interval, Cable Lock Up 45.As the clutch remains engaged, the capstan 68 holds the cable 64 in thedrawn state while the motor spins down. Because the worm screw 60 w andworm wheel 60 g will not allow pressure the brake pedal 9 exerts on thecable 64 to spin the capstan 68 backward to pay out the cable 64, thesystem continues to hold the brake pedal depressed and the capstan 68continues to hold that amount of the cable defined by the duration ofthe Motor Frame 44. As is graphically demonstrated by FIG. 6, the ClutchFrame 46 is the sum of the Programmed Clutch Delay 43, the Motor Frame44 and the Cable Lock Up 45. At a time 41 d, the control board 40terminates the Clutch Frame 46 releasing the capstan 68 from engagementwith the worm wheel 60 g through the clutch 62. The pressure in thetowed vehicle brake system and the influence of the brake return spring69 draw the cable 64 off of the capstan 68, returning the towed vehiclebrake system to an unactuated state.

A further interval exists. From the release of the capstan 68 at time 41c, until the duty cycle repeats which is the Cable Release 47 interval,making the system again receptive to pressure values from the pressuresensor 30. This too is a configurable variable and is designated, in thepreferred embodiment much as the Programmed Brake Delay 42 and is termedthe Cable Release 47 interval.

The preferred embodiment of the invention includes other designatableparameters that allow for adjustment in the operation of the instantinvention to enhance drivability and the modification of theseparameters might be by preprogrammed designation, user designation or,as discussed above, through artificial intelligence applied to readingsfrom accelerometers in either or both of the towing and to wed vehicles.Some of these configurable parameters might optionally include:

-   -   1) RESET DEFAULT VALUES—Selecting this option allows a        technician to reset each of the previously programmed values to        a factory designated default setting as might be stored in a        current version of firmware.    -   2) PROGRAM MAXIMUM PRESSURE—This parameter designates the        maximum pressure the pressure sensor 30 will accept as valid        rather than to indicate a device fault, e.g. ranges indicative        of air- or hydraulic-based braking in the towing vehicle.    -   3) PROGRAM MINIMUM PRESSURE—This parameter represents the        minimum pressure the pressure sensor 30 will accept as valid        rather than to indicate a device fault, e.g. ranges indicative        of air- or hydraulic-based braking in the towing vehicle.    -   4) PROGRAM APPLICATION PROPORTION PERCENTAGE—this parameter        designates the scope of cable 64 paid out or taken as the        difference between the maximum and minimum cable lengths        representing normal operation of the instant invention in this        particular towed vehicle.    -   5) PROGRAM MOTOR SPEED PERCENTAGE—Much as with the Programmed        Brake Delay 42, operation might prove that using the DC Motor at        speeds less than its maximum show demonstrable improvement in        either wear to the towed or towing vehicle brake systems or to        drivability in general and this parameter will decrease the        speed of the motor 60 as it takes up the cable 64 on the capstan        68.    -   6) PROGRAM ACTIVATION START THRESHOLD—This parameter sets a        minimum threshold where the braking operation in the towed        vehicle makes sense. For example, in driving, an operator might        wish to “feather” the brakes in the towing vehicle to correct or        ease steering. Braking in the towed vehicle might make that        maneuver a bit less intuitive. As such, it would not be        productive to have a slight pressure on the brakes of the towing        vehicle to set up a corresponding braking in the towed vehicle.        Further, if minor pressure fluctuations in the braking system of        the towing vehicle might best be ignored by the towed vehicle.    -   7) PROGRAM DEVICE DECREASE THRESHOLD—Corresponding to the        minimum threshold or Program Activation Start Threshold, this        parameter sets a threshold for the amount of pressure loss in        the towing vehicle brake system that must occur before the        device acts to release the cable.    -   8) PROGRAM TRAVEL INCREASE THRESHOLD—Finally, in the operating        range, this parameter determines the threshold for the amount of        pressure that would have to be added to an already pressurized        sensor before the device acts to take up more of the cable 64.    -   9) FULL BRAKE ENGAGEMENT MOTOR TIME—This parameter determines        the amount of time necessary for the motor 60 to pull the cable        64 causing the pedal 9 to translate through its full travel.

More designatable parameters might prove to be useful in otherembodiments of the invention. These are provided within this explanationin order to set forth the versatile and tailorable nature of thissupplementary braking system.

In FIG. 7, a flowchart 100, shows exemplary rudiments of operation bythe control board 40. Once the master switch 56 (FIG. 4) is closedenergizing the control board 40 allowing boot up at 105. After boot upat 105, the control board checks the voltage across the breakaway switch52 at 107 and if the breakaway switch 52 is open, at 109, the controlboard sends a signal to the clutch 62 and motor 60 consistent withapplication of the maximum braking force applied to the brake pedal 9(FIGS. 4, 5). To achieve this, the system draws the cable 64 to draw thepedal 9 to its minimum pedal height (FIG. 5). The brakes will not bereleased until the breakaway switch 52 is closed or the master switch 56is turned to the “off” position.

If the breakaway switch 52 is closed, the method proceeds, at 111, toacquire a pressure from the pressure sensor 30 by measuring thepotential across the sensor because of piezoresistance. In a 12-voltsystem, the most likely method will be by exploiting a voltage dividerwith a reference resistance. The reference resistor having a referenceresistance is placed in series with the pressure sensor. By knowing theratio, for example, that the potential across the reference resistorbears to a regulated 12 volts, the resistance of the piezoresistor inthe pressure sensor is known and by derivation, at 113, the pressure inthe towing vehicle braking system.

The resistance across the pressure sensor may optionally be converted toa pulse width modulated signal or may be expressed to the control board40, or by direct measurement, or by any other conventional manner but,the control board is made aware of the instantaneous pressure in thetowed vehicle braking system. Based upon that sensed pressure, at 111,each of a motor interval and a clutch interval are retrieved.(Throughout the remainder of this discussion, the terms “frame” and“interval” will be used interchangeably—each will refer to the periodthe control board sends an active signal to the respective devicecausing either of the motor to turn or the clutch to engage.). Thevalues are retrieved at 115 and these are translated into clutch andmotor frames at 117.

Given the tremendous reduction the worm screw 60 s and the worm wheel 60g perform in transmitting torque from the motor 60 to the capstan 68,the interval in which each of the motor and clutch are together engagedin duration is very nearly proportionate to the scope of cable 64 themotor 60 winds around the capstan 68. This is to say that except at theextreme, the effects of friction and pressure within the towed vehiclebrake system are such as to provide a nearly linear relationship. Inmuch of the operating range, then, the duration of the interval whenboth brake and clutch are engaged will, be the important metric forquantifying braking. More time engaged means more cable 64 is woundaround the capstan 68 and consequently the pedal 9 is drawn to a pedalheight much closer to the floor pan. The closer the pedal 9 is drawn tothe floorpan, the more pressure the towed vehicle exerts on the brakepads that stop the vehicle.

In operation, then, a proportion to the pressure sensed is determined bythe settings of the software in the control board. By way of nonlimitingexample, consider that for simplification of the explanation, the lookupvalues are set to be exactly proportionate to the pressure in the towingvehicle braking system. Then, by way of example, a hydraulic brakesystem in the towing vehicle has an operating range of between 0 psi to3000 psi and a maximum cable travel of four inches (4″). When thepressure sensor indicates a pressure of 1500 psi then, in concert, themotor 60 and clutch 62 would, in response to signals from the controlboard 40 draw the cable 64 to reduce the pedal height by two inches(2″). A reduction of the pressure in the towing vehicle braking systemto 1200 psi would cause the motor 60 and clutch 62 to draw the cable 64one and ⅗ inches (1.6″). An increase of pressure to a full 3000 psiwould result in the cable 64 being drawn the full four inches (4″).

As described herein, the presently preferred relationship betweenpressure sensed and pedal travel is linear, though the invention is notlimited to a strictly linear relationship between pressure and pedaltravel. For example, the processor 40 might also include a linear motionencoder attached to a slide receiver such as is used in electronic surgebraking systems in the tow bar. When rates of deceleration of the towingand towed vehicle differ, the slide receiver either extends or contractsto accommodate the distinct rates of deceleration of the two vehicles.The processor can then amend the values stored within the look up tablesto increase or to decrease the motor and clutch frames to yield brakingfunctions that exert the minimal extension or compression of the slidereceiver during braking, thereby assuring optimal stopping distances asthe deceleration characteristics of neither vehicle will tend todominate the other.

A preferred embodiment of the invention is depicted in FIG. 8 anddiffers from the more generalized embodiment depicted in FIG. 5 by thegraphic addition of two components which collectively act as a rotaryencoder also known as a shaft encoder. An optical rotary encoder isshown for explanatory purposes but nothing limits application to opticalencoders. A rotary encoder sensor assembly 74 is configured andpositioned in this nonlimiting example to read three concentric ringsdrawn on a rotary encoder rotor 72. In this example, the rotary encoderrotor 72 shows sectors of three concentric rings imprinted on a diskaffixed to the capstan 68. The pattern of the rings on the rotaryencoder rotor 72 represents the position of the capstan 68 in 3-bitbinary. Considering that a full revolution of the capstan 68 can beexpressed as rotating through 360 degrees, a table dividing the rotationof the capstan into V or eight position states can be expressed thus:

Standard Binary Encoding Contact Sector 1 Contact 2 Contact 3 Angle 0off off off  0° to 45° 1 off off ON 45° to 90° 2 off ON off  90° to 135°3 off ON ON 135° to 180° 4 ON off off 180° to 225° 5 ON off ON 225° to270° 6 ON ON off 270° to 315° 7 ON ON ON 315° to 360°

The inner ring of the rotor (obscured by the position of the capstan 68)corresponds to readings of the rotor 72 by contact 1 of the rotaryencoder sensor assembly 74 as are compiled as the most significant digitin the table. In this exemplary configuration black sectors are selectedto represent an “on”. As shown zero degrees is positioned as pointinghorizontally and on the right-hand side, opposite the rotary encodersensor assembly 74, though the initial position is arbitrary. Also, asdepicted the binary addresses of the positions increase as the rotorturns in a counterclockwise direction past the sensors. Optical sensorsand light sources within rotary encoder sensor assembly 74 “read” eachof the sectors of the rings immediately adjacent to the sensors aseither “on” or “off” so that at any given time, the rotary encodersensor assembly 74 can determine, in this example, the rotationalposition of the capstan with an accuracy of±22.5 degrees, or 360degrees/8 sectors. Where greater accuracy is desired, more sensors yieldshorter sectors. Four sensors means 2⁴ or 16 sectors yielding twice theresolution or an accuracy of±11.25 degrees and so forth.

The rotary encoder the embodiment exploits is not limited to an opticaldecoder. In fact, the invention will perform with any electro-mechanicaldevice that converts the angular position or motion of a shaft or axleto an analog or digital signal. In practice, there are two main types ofrotary encoders and either will work; encoders are either absolute orincremental (also referred to as relative). The output of absoluteencoders indicates the current position of the shaft, making them angletransducers. The output of incremental encoders provides informationabout the motion of the shaft, which is typically further processedelsewhere into information such as speed, distance and position. Devicescontrolled by incremental encoders may have to “go home” to a fixedreference point to initialize the position measurement. But, one such“go home” position is the “at rest” or “zero percent activated” positionof the capstan 68 in the actuator. While the above-described embodimentis set out as an absolute encoder for purposes of clarity, those havingordinary skill in the art will readily perceive that algorithms willallow use of either to advantage and nothing in this disclosure isintended to limit the encoder to absolute encoders.

While selected for purposes of description, a reflective optical encoderis shown, there are also transmissive optical encoders, i.e. those thatemploy a light shining onto a photodiode through slits in a metal orglass disk. These are otherwise equivalent to their reflective cousins.The sensors perceive light when it passes through the rotor. While suchencoders are the most common technology and an acceptable solution,optical encoders are very sensitive to dust and dust might readily bepresent in the footwell of the “dinghy”.

Another variant on the optical encoder is the conductive encoder, ratherthan optically readable sectors, the sectors are embedded as conductivesectors on the capstan 68 or a series of circumferential copper sectorsor tracks are etched or deposited onto the rotor 72 attached to thecapstan 68. Contact brushes within the rotary encoder sensor assembly 74are arranged to sense the conductive areas as they pass. This form ofencoder however is less favored because of wear due to the brushescontinual contact with the moving rotor 72.

Just as the invention is not limited to conductive, transmissive orreflective encoders, the technology the rotary encoder employs is notlimited to optical-type encoders. For example, one alternate encoderconsidered is a rotary magnetic encoders which are, typically, small,inexpensive devices. Magnetic encoders are used in high-volumeapplications, such as vehicle antilock braking systems, or sophisticatedunits demanding motion control tasks, such as industrial automationsystems and medical equipment. Available variations are incremental andabsolute types; non-contact and bearing versions; and units in whichrotating unit and encoder body are effectively separate subcomponents.

Sensing of magnetic fields is accomplished by exploiting the Halleffect. The Hall effect exploits the production of a voltage difference(the Hall voltage) across an electrical conductor, transverse to anelectric current in the conductor and to an applied magnetic fieldperpendicular to the current. It was discovered by Edwin Hall in 1879.When passing through a magnetic field a test current will fluctuateupwards or downwards based upon orientation of the magnetic fieldrelative to the sensor. By alternating the orientation of magnets in therim of the capstan 68, the Hall effect sensor can count sectors as theypass. Consequently, Hall sensors containing 32-pole encoder wheelsgenerate 16 pulses per revolution.

To avoid the effects of dust, one technology that might be used to goodadvantage is that described as on-axis magnetic and typically uses aspecially magnetized 2 pole neodymium magnet attached to the motorshaft. Because it can be fixed to the end of the shaft, it can work withmotors that only have 1 shaft extending out of the motor body. Theaccuracy can vary from a few degrees to under 1 degree. Resolutions canbe as low as 1 degree or as high as 0.09 degree (4000 CPR). Such highaccuracy is useful but not necessary. Another magnetic rotary decodertechnology is known as off-axis magnetic and could readily be employed.In its most cost-effective embodiment, off-axis magnetic decoders userubber bonded ferrite magnets attached to a metal hub in a mannersimilar to the optical sectors or conductive traces set forth above.Such a configuration offers flexibility in design and low cost. Due tothe flexibility in many off axis encoder chips they can be programmed toaccept any number of pole widths so the chip can be placed in anyposition required for the application.

Magnetic encoders operate in harsh environments where optical encoderswould fail to work. Another such encoder that would also work in theharsh environment of the dinghy driver's foot well is a capacitiveabsolute encoder. In such an embodiment, an asymmetrical shaped disk isrotated within the encoder. Such a rotor might be shaped with a spiralperimeter to intrude further into the interspace between two electrodesas the shaft rotates. The presence of the metal disk changes thecapacitance between the electrodes in a predictable manner which can bemeasured and calculated back to represent an angular value.

Not only are there a number of different and suitable encoders but thereare also a variety of coding conventions that should be discussed. Theexample, above, relies upon standard binary encoding, that is torepresent the eight sectors by the eight binary values in ascendingorder. But, not all encoders represent position in that manner. There isa drawback in that unless the contacts are perfectly aligned or if therotor 72 stops between two adjacent sectors, or the contacts are notperfectly aligned, the value sensed may not accurately reflect the trueposition of the shaft.

Referring to the truth table above, consider what happens when the shaftangle changes from 179.9° to 180.1° (from sector 3 to sector 4). At someinstant, according to the truth table, the contact pattern changes fromoff-on-on to on-off-off, meaning each of three sensors must change stateto measure a single sector change. It is only when all of the contactsare perfectly aligned, that all three contacts can change statesimultaneously to produce a smooth movement from sector 3 to sector 4.

In a practical device, the contacts are never perfectly aligned, so, inpractice, each of the switches changes state at a different moment. Ifcontact 1 switches first, followed by contact 3 and then contact 2, forexample, in a very short scope of rotation, the actual sequence of codeswould change from off-on-on (starting position) to on-on-on (first,contact 1 switches on), then to on-on-off (next, contact 3 switches off)arriving, finally at on-off-off (contact 2 switches off). To theprocessor reading from the encoder, in this example, the sectors thesensor assembly reads are, in sequence, 3, 7, 6 and then 4. So, from thesequence of codes produced, the shaft appears to have jumped from sector3 to sector 7, then gone backwards to sector 6, then backwards again tosector 4, which is where we expected to find it. Such information wouldbe very difficult for the inventive braking system to use in thisembodiment, and generating the above-described confusion is unnecessary.For this reason, the preferred embodiment of the invention would exploita known convention called Gray encoding.

The rotary encoder rotor for angle-measuring devices marked in 3-bitbinary-reflected Gray code (BRGC) differs from standard binaryannotation. Using BRGC in this ongoing example, the inner ringcorresponds to Contact 1 as in the standard binary table. Rememberingthat the inner ring corresponds to the most significant digit, i.e. 2³or 8, the sectors of the inner ring simply split the circular path intotwo halves. Then, it is the purpose of the second ring to split each ofthese two sectors in half but transitions cannot occur where the innerring splits the sector. Thus, in BRCG, the second ring or middle ringsimply replicates the inner ring but is offset by 90 degrees. As oneimagines it, these two rings will divide a single rotation into foursectors but only one ring will trigger at a time. Thus, just as in thebinary coding example, two sensor can divide the rotation into foursectors, but that division occurs without requiring simultaneoustransitions on the two rings.

Because we are using three contacts in this example, we can furtherdivide each of the four sectors the first two rings define into twohalves, however this division will alternate so that the second half ofa sector will have the same value as the first half of the next sectorso that the transition will not occur at any of the four sector lines.Thus, there are only four transitions in the BRCG third ring and theyoccur in the centers of each of the sectors the first two rings define.Thus, a four-sector ring having transitions offset by 45 degrees fromthose of the middle or inner rings would serve. For the three-contactexample given above, the Gray-coded version of the truth table would beas follows:

Gray Encoding Contact Sector 1 Contact 2 Contact 3 Angle 0 off off off 0° to 45° 1 off off ON 45° to 90° 2 off ON ON  90° to 135° 3 off ON off135° to 180° 4 ON ON off 180° to 225° 5 ON ON ON 225° to 270° 6 ON offON 270° to 315° 7 ON off off 315° to 360°

In this example, the transition from sector 3 to sector 4, like allother transitions, involves only one of the contacts changing its statefrom on to off or vice versa. This means that the sequence of incorrectcodes shown in the previous illustration cannot happen.

A further refinement that may be advantageously exploited is the use ofsingle-track Gray encoding. Just as the first two bits of the Grayencoded three-bit code can be generated by simply offsetting one sectorpattern by ninety degrees, the result is to create four distinctly codedsectors. If the most significant bit is rotated enough, it exactlymatches the next ring out. Since both rings are then identical, theinner ring can be omitted, and the sensor for that ring moved to theremaining, identical ring (but offset at that angle from the othersensor on that ring). Those two sensors on a single ring make aquadrature encoder with a single ring. Using a similar rationale, it ispossible to arrange several sensors around a single track (ring) so thatconsecutive positions differ at only a single sensor; the result is thesingle-track Gray code encoder.

Referring again to FIG. 8, regardless of the type of sensors or encodingstandard used by the encoder, we will, for discussion's sake, assumethat rotary encoder sensor assembly 74 and the encoded rotor 72cooperate to effect a meaningful encoder. Once the actuator 22 isinstalled, the actuator will perform a calibration; in the preferredembodiment, this calibration will be automatic and performed as a partof the boot-up. The actuator will note two important positions of thecapstan 68 and, thus, the encoded rotor 72, as that position isrecognized by the rotary encoder sensor assembly 74. The first of thesetwo positions is that of the very onset of brake application and thesecond is the state of maximum brake application. Ideally, the first ofthese is a position where no brake application has yet occurred by thecapstan 68, has wound sufficiently to tension the cable 64 and to “takeup the slack” as may exist in the pedal assembly itself; such a positioncorresponding to the “zero percent activated” position referred to aboveand, importantly does not, in such a position, cause contact between thebrake rotors and pads in the dinghy's braking system. So defined, allbraking in the dinghy occurs as the capstan 68 rotates between these twopoints.

Once the entire range of brake pedal travel, sensed by capstan position,is defined as occurring between these two points, the preferredembodiment defines braking of the dinghy as a function connecting thesetwo points. While it is envisioned that the processor 40 includes amemory on which may reside several specific automobile profiles, eachthat represents an optimal braking of a specific vehicle serving as adinghy, in the presently preferred embodiment, a generic profile is alinear function between the two points. This generic profile is used todefine the relationship between applied brake pedal travel as a functionof the specific sensed pressure at the pressure sensor 30 (FIGS. 3 and4). Thus, in the preferred embodiment the gearhead motor 56 turning thecapstan 68 through the clutch 62, will rotate the capstan 68proportionately to the sensed pressure at the pressure sensor 30.

Just as explained relative to FIGS. 4, 5 and 6, the electromagneticclutch 62 (FIG. 4) is interposed to allow the capstan 68 either to drawthe cable 64 when engaged or to freewheel paying out the cable 64 whendisengaged. When the control board 40 (FIG. 4) sends a current toactuate the clutch 68, the capstan 68 is accelerated to match the speedof the worm wheel 60 g. If the motor 60 is spinning, engagement of theclutch 62 will cause the capstan 68 to take up cable 64 drawing thebrake pedal 9 through its pedal height toward the floor pan. When theclutch 62 (FIG. 4) stops receiving the current from the control board40, the capstan 68 is free to rotate and the force the return spring 69exerts draws the cable 64 back off of the capstan 68 to an “at rest”position. U sing this alternate engagement and disengagement of theclutch, the system 20 (FIG. 4) can rotate the capstan 68 to rest at aspecific rotational position as dictated by the sensed pressure at thepressure sensor 30. In turn, as explained above, rotation of the capstanto a specific rotational position proportionally applies the brakes ofthe dinghy.

The encoder sensor 74 provides, as feedback, the rotational position ofthe capstan 68. As shown in FIG. 9 (FIG. 9 differs from FIG. 4 only bythe addition of the encoder rotor 72, the encoder sensor 74 and anencoder sensor trace 76), the encoder sensor trace 76 communicates therotational position of the capstan 68 to the controller 40. Using thefeedback information provided through the encoder sensor trace 76, thecontroller 40, then, can precisely depress the brake pedal 9 to applypressure as the sensed pressure at the pressure sensor 30 in the towingvehicle brake line dictates. As such, the dinghy applies the mostefficient braking so that the dinghy neither drags the towing vehiclenor overruns it in operation. By way of nonlimiting example, if thebrake pressure of the towing vehicle calls for 50% brake pedalapplication and the brake was already applied at 25% from the previouspressure reading, then the brake would apply only that additional 25% toachieve the 50% brake application that is now being called for.

In operation, the encoder sensor provides a signal analogous to that ina phase-locked loop system in signal processing. The operation of aphase locked loop, PLL, is based around the idea of comparing the phaseof two signals and then adjusting to minimize the phase differencebetween the two signals. This information about the phase differencebetween the two signals is then used to control the frequency of one ofthe signals to coincide with that of the other. In a similar manner, thedifference between where the system believes the brake pedal of thedinghy is and were it actually is, is the analog to the error in phaseor phase difference.

The system assures that the pedal displacement in the towed vehiclecorresponds with the sensed pressure at the pressure sensor 30. Theprocessor 40 employs an iterative process to assure that the percentageof the rotational range of the capstan 68 corresponds to the percentageof full pressure braking in the towing vehicle. The processor 40compares the rotational position of the capstan 68 to the anticipatedrotational position as dictated by the sensed pressure and the generatesan adjustment value according to the magnitude and sign of thedifference between the two values.

The inventive braking system having the rotary encoder exploits a methodthat differs slightly from that depicted in FIG. 7, above, and isdepicted in this FIG. 10. Pressure within the brake lines in the towingvehicle changes the resistance in a sensing circuit in a known,repeatable, and predictable fashion. Thus, in the inventive system, foreach resistance value measured across the pressure sensor, there is aunique value representing the appropriate depression of the brake pedalin the towed vehicle. The exact function that maps resistance across thepressure sensor onto brake pedal displacement values for optimal brakingis selected to minimize differences in decelerating the two vehicles toachieve optimally shortened braking distances. Based upon that sensedpressure, at 111, each of a motor interval and a clutch interval areretrieved. (Throughout the remainder of this discussion, the terms“frame” and “interval” will be used interchangeably-each will refer tothe period the control board sends an active signal to the respectivedevice causing either of the motor to turn or the clutch to engage.).The values are retrieved at 115 and these are translated into clutch andmotor frames at 117.

As described above, the interval in which each of the motor and clutchare together engaged in duration is very nearly proportionate to thescope of cable 64 the motor 60 winds around the capstan 68. This is tosay that except at the extreme, the effects of friction and pressurewithin the towed vehicle brake system are such as to provide a nearlylinear relationship. In much of the operating range, then, the durationof the interval when both brake and clutch are engaged will be theimportant metric for quantifying braking. More time engaged means morecable 64 is wound around the capstan 68 and consequently the pedal 9 isdrawn to a pedal height much closer to the floor pan. The closer thepedal 9 is drawn to the floor pan, the more pressure the towed vehicleexerts on the brake pads that stop the vehicle. As in the example above,a hydraulic brake system in the towing vehicle has an operating range ofbetween 0 psi to 3000 psi and wherein to brake the towed vehicle at amaximum rate requires a cable travel of four inches (4″). When thepressure sensor indicates a pressure of 1500 psi then, in concert, themotor 60 and clutch 62 would, in response to signals from the controlboard 40 draw the cable 64 to reduce the pedal height by two inches(2″). A reduction of the pressure in the towing vehicle braking systemto 1200 psi would cause the motor 60 and clutch 62 to draw the cable 64one and ⅗ inches (1.6″). An increase of pressure to a full 3000 psiwould result in the cable 64 being drawn the full four inches (4″). But,without feedback, the processor 40 cannot confirm the exactcorrespondence between pressure in the towing vehicle brake line anddeflection of the brake pedal in the towed vehicle.

In this presently preferred embodiment, the encoder sensor assemblyprovides values indicative of pedal position to allow adjustment offrame values to optimize those frame values. Given the processor'sknowledge of the towed vehicle's “zero percentage” brake application andthe maximum brake application, frame values can be adjusted so thatpressure in the towing vehicle braking system to more accuratelycorrespond to designed pedal travel values.

In practice, operation of the system accords largely with the operationof the nonlimiting exemplary system as described in FIG. 7. However,additional steps after block 125 are preformed to enhance the operationof the system under this presently preferred embodiment. When braking,at a block 127, the rotational encoder sensor 74 measures aninstantaneous value for the rotational position of the capstan 68. Thisthe processor 40 pairs with a corresponding instantaneous value forpressure (adjusted for latency in the system). Then, at a block 129,drawing from a look-up table, the processor compares the actualrotational position of the capstan 68 to the stored value correspondingto the measured instantaneous pressure In the braking system of thetowing vehicle to calculate a difference having a magnitude and sign.

At a block 131, guided by the difference, the processor amends thestored values for each of the motor and clutch frames to minimize thatdifference by an iterative process. At a block 133, the adjusted valuesare stored, replacing the retrieved values In the look-up table. As thesystem homes in on the optimal braking pressure in the towed vehicle,the calculated differences will fall below a threshold value therebyobviating the need for adjustment.

Importantly, however, the system also compensates for expansion due toambient temperature, stretch in the cable, or slight differences inmounting angle and position. Over time, the system can adjust to assurethat the rotation of the capstan 68 precisely corresponds to theanticipated values for pedal depression.

While the preferred embodiment of the invention has been illustrated anddescribed, as noted above, many changes can be made without departingfrom the spirit and scope of the invention. Accordingly, the scope ofthe invention is not limited by the disclosure of the preferredembodiment. Instead, the invention should be determined entirely byreference to the claims that follow.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A system for braking aflat-towed vehicle based upon a braking pressure of a braking fluid in abraking circuit in the towing vehicle, the system comprising: a piezoresistor mounted to sense braking pressure within the braking circuitand comprising one leg of a voltage divider, thereby to present a piezoresistor voltage drop across the piezo resistor, the piezo resistorvoltage drop corresponding to the braking pressure within the brakingcircuit; and a motor to actuate a brake system of the flat-towedvehicle, the motor including a motor output shaft, the motor outputshaft; an electromagnetic clutch for coupling, at its clutch input, themotor output shaft to, at its clutch output; a capstan; a rotary encoderfor sensing the rotational position of the capstan; a controller toretrieve a vehicle profile look up table, the vehicle profile look-upincluding each of the motor frame duration being a function of thesensed piezo resistor voltage drop and an anticipated rotationalposition as a function of motor frame duration the controller including:a switching network to effect: initiating a clutch frame, energizing aclutch to engage a motor output shaft; initiating a motor frame uponexpiration of a programmed clutch delay, energizing a motor to rotatethe motor output shaft in response to a signal from the controller; uponexpiration of the motor frame duration, receiving a signal from therotary encoder indicating an instantaneous rotational position of thecapstan immediately prior to interrupting the power to the motor;comparing the instantaneous rotational position of the capstan to theanticipated rotational position of the capstan to produce a rotationalposition difference; and storing an altered anticipated rotationalposition to replace the anticipated rotational position associated withthe motor frame duration in the vehicle profile, the altered motor frameduration being based upon the motor frame duration and the rotationalposition difference.
 2. The system of claim 1, wherein the motor is agearhead motor and comprises a motor driving a reduction gear train tomultiply torque at the motor output shaft relative to the torquegenerated by a motor rotor the motor includes by a factor exceeding fourtimes.
 3. The system of claim 2, wherein the reduction gear train isselected from a group consisting of a worm and worm gear train; aplanetary gear train; a bevel gear train; a pinion and spur gear train;a helical gear train; and a double helical gear train.
 4. The system ofclaim 2, wherein the switching network further effects: upon terminationof the motor frame, continuing engagement of the clutch until theexpiration of a cable lock up frame terminating the clutch frame byreleasing engagement of the clutch.
 5. The system of claim 1, wherein acable wraps the capstan and is connected to a towed vehicle brake pedalsuch that upon engagement of the clutch, rotation of the motor outputshaft rotates the capstan to take up the cable and, thereby, to draw thetowed vehicle brake pedal in a manner to actuate the towed vehiclebraking system, engaging the towed vehicle brakes.
 6. The system ofclaim 1, wherein retrieving a motor frame duration based upon themeasured piezoresistor voltage drop further includes: populating thelookup table with a multiplicity of motor frame durations, each motorframe duration being associated with at least one piezoresistor voltagedrop; and indexing the multiplicity of motor frame durations forretrieval based upon a selected piezoresistor voltage drop.
 7. Thesystem of claim 6, wherein populating a lookup table with a multiplicityof motor frame durations, each motor frame duration being associatedwith at least one piezoresistor voltage drop further includes:initializing the lookup tables with initial estimates of the motor frameduration being associated with at least one piezoresistor voltage drop;retrieving a first motor frame duration based upon a measuredpiezoresistor voltage drop; measuring at least one of deceleration ofthe towing vehicle and brake temperature of towed vehicle brakingsystem, based upon the use of the first motor frame duration; generatinga second motor frame duration based upon the measured piezoresistorvoltage drop, the second motor frame duration being distinct from thefirst motor frame duration by an integral multiple of a selected motorframe duration increment; measuring the at least one of deceleration ofthe towing vehicle and brake temperature of towed vehicle brakingsystem, based upon the use of the first motor frame duration comparingthe first motor frame duration to the second motor frame duration todetermine a new first motor frame duration solution based upon themeasured values of the at least one of deceleration of the towingvehicle and brake temperature of the towed vehicle braking system;continue to vary the first motor frame duration by distinct integralmultiples of the selected motor frame increment to develop a pluralityof solutions; evaluating the plurality of solutions until said at leastone of said plurality of solutions determines a local minimum the atleast one of deceleration of the towing vehicle and brake temperature ofthe towed vehicle braking system; and store the first motor frameduration associated with the local minimum of the at least one ofdeceleration of the towing vehicle and brake temperature of the towedvehicle braking system as the motor frame duration associated with theat least one piezoresistor voltage drop.
 8. The system of claim 1,further comprising a mechanism to: compare deceleration of the towedvehicle relative to the towing vehicle while the braking.
 9. A methodfor braking a flat-towed vehicle based upon a braking pressure of abraking fluid in a braking circuit in the towing vehicle, the methodcomprising: measuring a piezoresistor voltage drop across apiezoresistor positioned within the braking circuit such that thepiezoresistor voltage drop changes in response to the braking pressurewithin the braking circuit; retrieving a motor frame duration based uponthe measured piezoresistor voltage drop; engaging a clutch to a motoroutput shaft to initiate a clutch frame, the clutch having a clutchinput attached to the motor output shaft and a clutch output attached toa capstan; upon expiration of a programmed clutch delay, initiating amotor frame by supplying power to a motor to rotate the motor outputshaft and the engaged clutch; continuing to supply power to the motor torotate the motor output shaft and the engaged clutch throughout themotor frame duration; and upon expiration of the motor frame duration,storing a sensed rotational position of the capstan and, upon sensing,terminating the motor frame by interrupting the power to the motor. 10.The method of claim 9, wherein the motor is a gearhead motor andcomprises a motor driving a reduction gear train to multiply torque atthe motor output shaft relative to the torque generated by a motor rotorthe motor includes by a factor exceeding four times.
 11. The method ofclaim 10, wherein the reduction gear train is selected from a groupconsisting of a worm and worm gear train; a planetary gear train; abevel gear train; a pinion and spur gear train; a helical gear train;and a double helical gear train.
 12. The method of claim 10, wherein themethod further comprises: upon termination of the motor frame,continuing engagement of the clutch until the expiration of a cable lockup frame to terminate the clutch frame by releasing engagement of theclutch.
 13. The method of claim 9, wherein a cable connects the capstanto a towed vehicle brake pedal such that upon rotation of the capstan,the cable is taken up drawing the towed vehicle brake pedal downward ina manner to activate the towed vehicle braking system, engaging thetowed vehicle brakes.
 14. The method of claim 9, wherein retrieving amotor frame duration based upon the measured piezoresistor voltage dropfurther includes: populating a lookup table with a multiplicity of motorframe durations, each motor frame duration being associated with atleast one piezoresistor voltage drop; indexing the multiplicity of motorframe durations for retrieval based upon a selected piezoresistorvoltage drop; generating an anticipated rotational position of thecapstan associated with each motor frame duration.
 15. The method ofclaim 14, wherein populating a lookup table with a multiplicity of motorframe durations, each motor frame duration being associated with atleast one piezoresistor voltage drop further includes: initializing thelookup tables with initial estimates of the motor frame duration beingassociated with at least one piezoresistor voltage drop; retrieving afirst motor frame duration based upon a measured piezoresistor voltagedrop; measuring at least one of deceleration of the towing vehicle andbrake temperature of towed vehicle braking system, based upon the use ofthe first motor frame duration; generating a second motor frame durationbased upon the measured piezoresistor voltage drop, the second motorframe duration being distinct from the first motor frame duration by anintegral multiple of a selected motor frame duration increment;measuring the at least one of deceleration of the towing vehicle andbrake temperature of towed vehicle braking system, based upon the use ofthe first motor frame duration comparing the first motor frame durationto the second motor frame duration to determine a new first motor frameduration solution based upon the measured values of the at least one ofdeceleration of the towing vehicle and brake temperature of the towedvehicle braking system; continue to vary the first motor frame durationby distinct integral multiples of the selected motor frame increment todevelop a plurality of solutions; evaluating the plurality of solutionsuntil said at least one of said plurality of solutions determines alocal minimum the at least one of deceleration of the towing vehicle andbrake temperature of the towed vehicle braking system; and store thefirst motor frame duration associated with the local minimum of the atleast one of deceleration of the towing vehicle and brake temperature ofthe towed vehicle braking system as the motor frame duration associatedwith the at least one piezoresistor voltage drop.
 16. The method ofclaim 15, wherein the at least one of deceleration of the towing vehiclerelative to the towed vehicle, tensile stress the connection betweentowing vehicle and the towed vehicle and brake temperature of the towedvehicle braking system are measured at a selected piezo resistor voltagedrop during braking by the towing vehicle and the motor frame durationassociated with that piezo resistor voltage drop.
 17. A supplementalbraking system for a towed vehicle, the system comprising: a controller,the controller being responsive to a signal from the towing vehicleindicating application of the towing vehicle braking system, thecontroller including a switching network connected to: receive a sensedcapstan rotational position; selectively activate a clutch; andselectively energize a motor; the motor having a motor output shaftconnected to the clutch, the motor rotating when energized by theswitching network; the clutch, engaged when activated by the switchingnetwork, the clutch rotates with the motor output shaft; a capstanattached to the clutch such that the capstan rotates with the motoroutput shaft when the clutch is engaged; a rotary encoder to sense thecapstan rotational position; and a cable connecting the capstan to abrake pedal in the towed vehicle, such that when the capstan rotates thecable draws the brake pedal to engage brakes in the towed vehicle. 18.The supplemental braking system for a towed vehicle of claim 17, whereinthe signal from the towing vehicle indicating application of the towingvehicle braking system is a change in a piezoresistor voltage drop, thepiezoresistor being mounted inside of the towing vehicle braking circuitto sense a pressure of a braking fluid in the towing vehicle brakingcircuit.
 19. The supplemental braking system for a towed vehicle ofclaim 17, wherein the cable is selected from a group consisting of awire rope, wire rope and pulley, a flexible nylon rack, a flexible nylonconnector, a tie rod, a tape, and a Bowden cable.
 20. The supplementalbraking system for a towed vehicle of claim 17, wherein the controlleractivates the switching network to effect the following: initiating aclutch frame, energizing a clutch to engage a motor output shaft;initiating a motor frame upon expiration of a programmed clutch delay,energizing a motor to rotate the motor output shaft in response to asignal from the controller; upon expiration of the motor frame duration,sensing the capstan rotational position and terminating the motor frameby interrupting the power to the motor; and upon termination of themotor frame, continuing engagement of the clutch until the expiration ofa cable lock up frame terminating the clutch frame by releasingengagement of the clutch.
 21. The system of claim 20, wherein the motoris a gearhead motor and comprises a motor driving a reduction gear trainto multiply torque at the motor output shaft relative to the torquegenerated by a motor rotor the motor includes by a factor exceeding fourtimes.
 22. The system of claim 21, wherein the reduction gear train isselected from a group consisting of a worm and worm gear train; aplanetary gear train; a bevel gear train; a pinion and spur gear train;a helical gear train; and a double helical gear train.